Electronegative LDL induction of apoptosis in macrophages: Involvement of Nrf2

Abstract

The aim of this study was to determine the apoptotic pathways and mechanisms involved in electronegative LDL [LDL(−)]-induced apoptosis in RAW 264.7 macrophages and the role of Nrf2 in this process. Incubation of RAW 264.7 macrophages with LDL(−) for 24 h resulted in dose-dependent cell death. Activated caspases were shown to be involved in the apoptosis induced by LDL(−); incubation with the broad caspase inhibitor z-VAD prevented apoptosis in LDL(−)-treated cells. CD95 (Fas), CD95 ligand (FasL), CD36 and the tumor necrosis factor (TNF) ligand Tnfsf10 were overexpressed in LDL(−)-treated cells. However, Bax, Bcl-2 and Mcl-1 protein levels remained unchanged after LDL(−) treatment. LDL(−) promoted hyperpolarization of the mitochondrial membrane, elevated reactive oxygen species (ROS) production and translocation of Nrf2 to the nucleus, a process absent in cells treated with native LDL. Elicited peritoneal macrophages from Nrf2-deficient mice exhibited an elevated apoptotic response after challenge with LDL(−), together with an increase in the production of ROS in the absence of alterations in CD36 expression. These results provide evidence that CD36 expression induced by LDL(−) is Nrf2-dependent. Also, it was demonstrated that Nrf2 acts as a compensatory mechanism of LDL(−)-induced apoptosis in macrophages.